In a wireless communication apparatus such as mobile communications, a sampling filter apparatus that discretizes signals in terms of time, and carries out frequency conversion and filtering has been used. As a prior art sampling filter apparatus, for example, there was such an apparatus as disclosed in Patent Document 1. FIG. 10 shows the prior art sampling filter apparatus described in Patent Document 1.
In FIG. 10, the prior art sampling filter apparatus includes a mutual conductance amplifier 305, a history capacitor 307, rotating capacitors 308 and 309, switches 312, 314 and 315, and a digital control unit 317. The switches 312, 314 and 315 are controlled by signals generated by the digital control unit 317. An RF current output from the mutual conductance amplifier 305 is accumulated in the history capacitor 307, rotating capacitors 308 and 309, and a discrete-time sample stream is produced by cyclically reading the charge accumulated in the rotating capacitors 308 and 309. When resetting the charge accumulated in the rotating capacitors 308 and 309, an IIR filtering action is brought about.    Patent Document 1: JP-A-2004-289793 (Page 15, FIG. 3a)